Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking pan or line it with parchment paper.
Mix the melted butter and brown sugar until well combined.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
In another bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in the chocolate chunks.
Pour the batter into the prepared pan, spreading it evenly.
Bake for 25-30 minutes or until the edges are golden and a toothpick comes out clean.